Method of making semiconductor integrated-circuit capacitor

ABSTRACT

A semiconductor integrated-circuit capacitor comprises a lower electrode formed on a semiconductor substrate, a capacitor insulating film formed on the lower electrode, and an upper electrode formed on the capacitor insulating film. The capacitor insulating film is made of a high-permittivity material, and at least one of the upper and lower electrodes is made of a carbon film or a multilayered film composed of a carbon film and a conductor film other than carbon.

This is a division of application Ser. No. 08/094,422 filed on Jul. 16,1993 U.S. Pat. No. 5,440,157.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor integrated-circuitcapacitor and a method of manufacturing the same.

2. Description of the Related Art

As a type of semiconductor device adapted for information storage, thereis a dynamic random access read-write memory (DRAM) whose storage cellsare based on transistor-capacitor combinations. In a capacitor used in astorage cell in such a DRAM, as its electrodes use is made of amaterial, such as polysilicon, tungsten (w), molybdenum (Mo), oraluminum (Al). As an insulating film sandwiched between the twoelectrodes of the capacitor, serving as the capacitor insulating film(dielectric film), a silicon oxide film is used.

With recent rapid large-scale integration of such semiconductor devices,it has been required that the capacitance of capacitors be increased.With a conventional capacitor structure, this requirement will be met byreducing the thickness of silicon oxide film used as an insulating filmto a great extent because silicon oxide is low in permittivity ordielectric constant. However, reducing the thickness of the capacitorinsulating film too much will result in an increase in current leakage.

For this reason, instead of reducing the thickness of the capacitorinsulating film, the use of an insulating film having higherpermittivity than the silicon oxide film is now being considered.Specifically, metal compounds including perovskite dielectric material,such as tantalum pentoxide, PZT(Pb(Ti, Zr)O₃), etc., are underconsideration. The dielectric constant of tantalum pentoxide film isapproximately seven times as high as the dielectric constant of siliconoxide film.

On the one hand, however, these metal compounds exhibit highpermittivity, but on the other hand they are small in forbidden bandwidth (band gap) and hence have a poor insulating capability.Consequently, the use of these materials as a capacitor insulating filmwould also cause an increase in leakage current. In other words, theinsulating film formed of such a high-permittivity material as describedabove has a considerably poor capability of retaining charges, whichreduces the charge retaining capability of capacitors and hencedecreases the reliability of DRAMs.

SUMMARY OF THE INVENTION

It is therefore a first object of the present invention to provide asemiconductor integrated-circuit capacitor which uses high-permittivitymaterial as its capacitor insulating film to increase its capacitanceand can reduce its leakage current.

It is a second object of the present invention to provide a method ofproducing a semiconductor integrated-circuit capacitor in which itscapacitor insulating film is formed of a high-permittivity material inorder to increase its capacitance while its leakage current is low.

The first object of the present invention is attained by a semiconductorintegrated-circuit capacitor comprising a lower electrode formed on asemiconductor substrate, a capacitor insulating film formed on saidlower electrode, and an upper electrode formed on said insulating film,said capacitor insulating film comprising a high-permittivity material,and at least one of said upper electrode and said lower electrodeconsisting of a carbon film or a multilayered film composed of a carbonfilm and a conductor film other than carbon.

The second object of the present invention is attained by a method ofmanufacturing a semiconductor integrated-circuit capacitor comprisingthe steps of: forming a capacitor lower electrode on a semiconductorsubstrate; forming a capacitor insulating film of a high-permittivitymaterial on said capacitor lower electrode; annealing said capacitorinsulating film in a gas atmosphere containing excited oxygen; andforming a capacitor upper electrode on said capacitor insulating filmthat has been annealed.

The second object of the present invention is also attained by a methodof manufacturing a semiconductor integrated-circuit capacitor comprisingthe steps of: forming a capacitor lower electrode on a semiconductorsubstrate; forming a capacitor insulating film of a high-permittivitymaterial on said capacitor lower electrode; and forming a carbon film asa capacitor upper electrode on said capacitor insulating film at atemperature of 300° C. or more.

The present invention may preferably be adapted for stacked capacitorsbut can be adapted for different capacitors such as trench capacitors.

Additional objects and advantages of the invention will be set forth inthe description which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and obtained by means ofthe instrumentalities and combinations particularly pointed out in theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate presently preferred embodiments ofthe invention and, together with the general description given above andthe detailed description of the preferred embodiments given below, serveto explain the principles of the invention.

FIG. 1 shows a relationship between the permittivity and forbidden bandwidth of various dielectric materials;

FIG. 2 is an energy-band diagram when tantalum pentoxide film is used asthe capacitor insulating film, and one (the lower electrode) ofcapacitor electrode consists of an n⁺ silicon film and the other (theupper electrode) consists of one of various conductor films;

FIGS. 3A to 3D are sectional views which collectively show a process, inthe order of steps of the process, of manufacturing anintegrated-circuit capacitor in accordance with a first embodiment ofthe present invention;

FIGS. 4A to 4D are sectional views which collectively show a process, inthe order of steps of the process, of manufacturing anintegrated-circuit capacitor in accordance with a second embodiment ofthe present invention;

FIGS. 5A to 5D are sectional views which collectively show a process, inthe order of steps of the process, of manufacturing anintegrated-circuit capacitor in accordance with a third embodiment ofthe present invention;

FIGS. 6A to 6C are sectional views which collectively show a process, inthe order of steps of the process, of manufacturing anintegrated-circuit capacitor in accordance with a fourth embodiment ofthe present invention;

FIGS. 7A to 7C are sectional views which collectively show a process, inthe order of steps of the process, of manufacturing anintegrated-circuit capacitor in accordance with a fifth embodiment ofthe present invention;

FIGS. 8A to 8C are sectional views which collectively show a process, inthe order of steps of the process, of manufacturing anintegrated-circuit capacitor in accordance with a sixth embodiment ofthe present invention;

FIG. 9 illustrates an annealing device used in Example 4;

FIG. 10 illustrates an annealing device used in Example 5;

FIG. 11 illustrates an annealing device used in Example 6;

FIG. 12 is a graph illustrating leakage characteristics of the capacitoraccording to the second embodiment of the present invention incomparison with a conventional capacitor;

FIG. 13 is a graph illustrating current leakage characteristics of thecapacitor according to the fourth embodiment of the present invention inrelation to several given temperatures at which the capacitor upperelectrode (carbon film) is formed;

FIG. 14 shows carbon-film work function versus carbon-film formingtemperature; and

FIG. 15 shows the leakage current suppressing effect for six types ofcapacitors manufactured under different conditions for comparison.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the present invention, in order to increase the capacitance of asemiconductor integrated-circuit capacitor, a thin film ofhigh-permittivity material is used as the capacitor insulating film.Examples of such high-permittivity materials include silicon nitride,tantalum pentoxide, zirconium dioxide (ZrO₂), hafnium dioxide (HfO₂),niobium pentoxide (Nb₂ O₅), lead titanate (PbTiO₃), lead zirconatetitanate (PZT), strontium titanate (SrTiO3), barium titanate (BaTiO3),etc. In order to increase the capacitance of the integrated-circuitcapacitor, it is particularly preferable that the dielectric film usedas a capacitor insulating film have an dielectric constant of 20 ormore.

In the integrated capacitor of the present invention, at least one oftwo capacitor electrodes is formed of a film of carbon. This permits theleakage current to be suppressed even when the capacitor insulating filmused is made of one of the above-described high-permittivity materials.Consequently, the capacitor of the present invention is permitted tohave very high capacitance due to its excellent ability to retaincharges, and reduced leakage current.

Hereinafter, this effect will be described in detail.

A capacitor, which aims to retain charges, is required to have both goodinsulation between two electrode thereof and high capacitance. In orderto ensure that the capacitor has a high capacitance, it is desired thatthe capacitor insulating film (dielectric film) be made of ahigh-permittivity material. However, the use of high-permittivitymaterial for the capacitor insulating film would deteriorate itsinsulating property.

In general, more dielectric material has narrower forbidden band. FIG. 1shows permittivity versus forbidden band width (band gap) for variousdielectric materials. This diagram is cited from "Thin Solid Films, 2"by P. j. Harrop and D. S. Campbell, p. 273 (1968). In a capacitor, whenthe forbidden band of an insulating-film material used is narrow, theenergy barrier between the insulating film and the capacitor electrode(i.e., electric conductor) will be low, which produces great leakagecurrent at the time of application of a voltage and thus deterioratesinsulation characteristic.

In order to obtain a high-performance capacitor conforming to the objectof the present invention, therefore, it is required not only to increaseits capacitance by the use of a high-permittivity capacitor insulatingfilm but also to reduce leakage current by making high the energybarrier between the insulating film and the capacitor electrode tothereby improve the insulation characteristic.

Those situations for the case where tantalum pentoxide is used forcapacitor insulating film will be explained in detail as follows. Thedielectric constant (relative permittivity) of tantalum pentoxide isabout 28, which is much greater than that of silicon dioxide, i.e., 3.9.However, the forbidden band width of tantalum pentoxide is about 4.5 eV,which is smaller than that of silicon dioxide, i.e., 8 eV. For thisreason, the tantalum pentoxide film will producethermal-excitation-dependent carrier conduction (P - F type conduction)through trap sites in the film and is thus inferior to silicon dioxidefilm in terms of insulation characteristic. In order to use tantalumpentoxide for the capacitor insulating film, therefore, it is requiredto use a special means of suppressing leakage current. As a basic means,therefor, the present invention adopts a means of making the energybarrier between the tantalum pentoxide film and the capacitor electrodematerial higher.

FIG. 2 is an energy band diagram when tantalum pentoxide is used for thecapacitor insulating film, and an n⁺ silicon film is used as one (lowerelectrode) of two capacitor electrodes which are insulated from eachother by the insulating film and an aluminum (Al) film, tungsten (W)film or carbon film is used as the other (upper electrode) of thecapacitor electrodes. As can be seen from FIG. 2, the deeper the Fermilevel of the conductor electrode is, in other words, the greater thework function value of the conductor electrode is, the higher the energybarrier φ_(B) between the capacitor insulating film and the the upperelectrode is. The height of the energy barrier is equal to the depth ofthe Fermi level of the conductor plate (upper electrode) when theuppermost energy level of the forbidden band width Eg of the capacitorinsulating film (tantalum oxide) is referred to. The higher the barrierφ_(B) is, the lower the current leakage is. The leakage currentsuppressing effect due to the energy barrier φ_(B) is appeared moresignificantly when the forbidden band of the insulating film formingmaterial is narrower, in other words, when the permittivity of thecapacitor insulating film is higher. When use is made of a capacitorinsulating film which, like tantalum pentoxide film, is higher inpermittivity and narrower in forbidden band than silicon dioxide film,therefore, it is remarkably effective to use an electrode materialhaving a greater work function in order to maximize the effect ofsuppressing the leakage current.

As examples of such materials having great work functions, there arenoble metals such as platinum (Pt), etc. The platinum has a workfunction of 5.4 eV. However, problems with these noble metals are thatthey are difficult to be formed into a film and to be processed into anelectrode pattern. In contrast, the carbon film used in the presentinvention as the capacitor electrode is excellent in these respects. Asshown in FIG. 2, the work function of the carbon film is about 5 eV,which is greater than that of aluminum film (4.3 eV) and that oftungsten film (4.5 ev). As a result, the energy barrier height φ_(B) incase of the carbon film being used as the capacitor electrode is 2.5 eV,which is greater than that (1.8 ev) wherein the aluminum film is usedand that (2.2 eV) wherein the carbon film is used. Consequently, the useof a carbon film as the capacitor electrode permits the leakage currentto be suppressed. The situation mentioned above is also applied to acase wherein a high-permittivity material other than tantalum pentoxideis used for the capacitor insulating film.

As described above, the capacitor of the present invention is permittedto have a high capacitance by the use of a high-permittivity materialfor the capacitor insulating film and to reduce leakage current by theuse of a carbon film as a capacitor electrode.

Carbon is not so larger in specific resistance in comparison with othermetals conventionally used as electrode materials. However, ifnecessary, use may be made of a multilayer film structure in which afilm or films of metals other than carbon are laminated on the carbonfilm, thereby adjusting the performance of the capacitor electrode.

In addition, the carbon film, serving as a capacitor electrode accordingto the present invention, can be formed by sputtering technique or achemical vapor deposition (CVD) that is excellent in step coverage forthe three-dimensional structure of a capacitor, and moreover, can beprocessed into a fine pattern by a reactive ion etching technique usingoxygen and the like as a reactive gas. Thus, the conventional LSImanufacturing processes can easily be applied to the manufacture of thecapacitors of the present invention.

Next, a manufacturing method of the semiconductor integrated-circuitcapacitor of the present invention will be described.

If the conventional LSI manufacturing process were applied unchanged tothe manufacture of a capacitor structured as described above, acapacitor insulating film of high-permittivity material would first beformed by sputtering or CVD, and a carbon film would then be formed onthe insulating film. In this case, a trace amount of hydrogen wouldinevitably be entrapped in the capacitor insulating film formed bysputtering or CVD. That is, in the case of sputtering, residual moistureand hydrogen left without being exhausted in the film forming chamberwould cause hydrogen to be entrapped in the capacitor insulating film.In the case of CVD, besides the residual moisture and hydrogen, the useof an organometal source in particular would cause more hydrogen to beentrapped in the insulating film.

When a carbon film is formed on the capacitor insulating film in whichhydrogen has been entrapped, a reaction will occur between hydrogen inthe insulating layer and carbon, thereby forming a hydrocarboncontaininglayer at the interface. The layer of hydrocarbon thus formed reducesadhesion between the carbon film and the capacitor insulating film,making the carbon film easy to peel off.

Furthermore, the formation of a hydrocarbon-rich layer at the interfacebetween the capacitor insulating film and the capacitor electrode willdegrade the electrical property of the capacitor. That is, thehydrocarbon layer formed at the interface is electrically unstable andthus acts as a high-resistance conductor at low frequencies or DC butcannot pursue high frequencies. As a result, the hydrocarbon layer atthe interface will form series capacitance, thus decreasing the apparentcapacitance of the capacitor.

As can be seen in the description mentioned above, hydrogen entrapped inthe capacitor insulating film remarkably reduces the yield of integratedcircuits and degrades the device performance. In order to solve suchproblems, the manufacturing method of the present invention employsannealing, in a gas atmosphere containing excited oxygen, of a capacitorinsulating film of a high-permittivity material before a carbon film isformed on it.

Here, the excited oxygen refers to oxygen in a higher energy state thanoxygen molecules in the ground state. Examples of the excited oxygeninclude oxygen ions (including molecular ions and atomic ions) andoxygen free-radicals (including molecular radicals and atomic oxygen).The atmosphere containing such excited oxygen can be obtained by oxygenplasma, discharge in oxygen gas, or irradiation of an ozone gas withultraviolet rays.

It is difficult to remove the hydrogen entrapped in the capacitorinsulating film by means of simple annealing because it combines withconstituent elements of the film. However, the use of an annealingmethod adopted by the present invention permits the hydrogen in questionto be extracted from the film forming elements and to be removed fromthe film by the action of the excited oxygen. More specifically, suchexcited oxygen is very active and will permeate the capacitor insulatingfilm at high temperatures. Consequently, when the annealing is carriedout at a sufficiently high temperature, the excited oxygen permeates thecapacitor insulating film and reacts with hydrogen contained in theinsulating film to form water molecules. The resultant water moleculesdiffuse to the outside and is thus removed. As a result, the formationof a carbon film after the annealing will avoid the peeling of thecarbon film and the degradation of the capacitor performance.

It has been revealed that the annealing is similarly effective for theuse of a metal other than carbon for the capacitor electrode, such astungsten, which has been used conventionally. Therefore, the presentinvention will also cover such embodiments.

The present invention includes a method of further suppressing theleakage current by improving the quality of the carbon film used as thecapacitor electrode in manufacturing the semiconductorintegrated-circuit capacitor. According to this method, the carbon filmis formed at a temperature of 300° C. or more. As will be describedlater, the inventors of the present invention have confirmed that theformation of the carbon film at such a high temperature makes its workfunction value greater. As a result, the energy barrier φ_(B) betweenthe capacitor electrode and the capacitor insulating film is madehigher, permitting the capacitor leakage current to be suppressed moreeffectively.

As described above, the present invention is intended to achieveincreasing the capacitance of a semiconductor integrated-circuitcapacitor by using a high-permittivity film as the capacitor insulatingfilm and, at the same time, suppress the leakage current of thecapacitor. To carry out the intention, the present invention disclosesthree means: (a) using a carbon film as a capacitor electrode, (b)annealing the high-permittivity film in an atmosphere of excited oxygen,and (c) forming the carbon film at a high temperature of 300° C. ormore. These means may be used individually or in combination. Forevaluating the effect of these means in comparison with the conventionalart, the following six types of capacitors were manufactured.

(1) Without annealing, tungsten electrode (conventional)

(2) Without annealing, carbon electrode (film forming temperature:ordinary temperature)

(3) Without annealing, carbon electrode (film forming temperature: hightemperature)

(4) With annealing, tungsten electrode

(5) With annealing, carbon electrode (film forming temperature: ordinarytemperature)

(6) With annealing, carbon electrode (film forming temperature: hightemperature)

The leakage current characteristics of the six types of capacitors weremeasured and the results shown in FIG. 15 were obtained. As can be seenfrom FIG. 15, although a certain effect over the conventional art can beobtained even when each of the three means is used alone, the combineduse of these three means produces a much greater effect.

Hereinafter, reference will be made to the drawings to describe thepreferred embodiments of the present invention, which are intended tofacilitate the understanding of the present invention and are thereforeillustrative only and not restrictive.

In the following description, semiconductor integrated-circuitcapacitors according to the embodiments of the present invention and themanufacturing processes therefor will be described together.

EXAMPLE 1

FIGS. 3A to 3D illustrate manufacturing steps for a capacitor accordingto a first embodiment of the present invention. The first embodiment isdirected to a DRAM having stacked capacitor cells each using an n⁺polysilicon film as the capacitor lower electrode (storage node), atantalum pentoxide film as the capacitor insulating film, and a carbonfilm as the capacitor upper electrode (plate electrode).

First, the major surface of a p-type silicon substrate having the (100)plane and a resistivity of 10 Ω·cm is selectively oxidized by means ofLOCOS (localized oxidation of silicon) to form a device isolation film102 consisting of a thermally grown thick oxide film. Next, a thin oxidefilm is thermally grown on the surface area surrounded by the film 102,and an n⁺ type polysilicon film is then deposited on the thin oxide filmby means of CVD. The two superposed films are patterned usingconventional photoresist masking and etching to form a gate oxide film103 and a gate electrode 104. Subsequently, the substrate 101 issubjected to ion implantation using the gate electrode 104 as a blockingmask, whereby n⁻ type regions 105₁ and 105₂, separated by a channelregion, are formed on a self-alignment basis (FIG. 3A). The n⁻ typeregions 105₁ and 105₂ serve as drain and source regions, respectively,of a MOS transistor.

Next, a thick CVD oxide film 106 serving as an interlayer insulatingfilm is formed over the entire surface of the substrate and thenpatterned by conventional photoresist masking and etching to form anopening 107 communicating with the n⁻ type region 105₁ (FIG. 3B).

Next, a second n⁺ polysilicon film is deposited and then patterned byconventional photoresist masking and etching to form an n⁺ typepolysilicon film pattern 108 which is in contact with the n⁻ type region105₁. Subsequently, if necessary, a very thin silicon nitride film 109may be formed on the polysilicon film pattern 108 by direct nitridationin order to prevent an oxide film from naturally growing on the pattern108 (FIG. 3C).

Next, a tantalum pentoxide film 110 is deposited by reactive sputtering,CVD, or another suitable film forming technique. Subsequently, a carbonfilm is formed on the tantalum pentoxide film 110 and then patterned byconventional photoresist masking and etching to form a carbon filmpattern 111 (FIG. 3D). Note that a trace amount of impurities of, forexample, an group III element such as boron (B), or a V group elementsuch as phosphorus (P) or arsenic (As), may be added to the carbon filmpattern 111 for the purpose of reducing its specific resistance.

In this manner a memory cell capacitor composed of the capacitor upperelectrode consisting of the polysilicon film pattern 108, the capacitorinsulating layer consisting of the tantalum pentoxide film 110, and thecapacitor upper electrode consisting of the carbon film pattern 111 iscompleted.

As usual, the LSI manufacturing process is followed by subsequent stepsincluding the formation of a passivation film, the formation ofinterconnection wires, etc.

EXAMPLE 2

FIGS. 4A to 4D illustrate manufacturing steps of a capacitor accordingto a second embodiment of the present invention. The second embodimentis directed to a DRAM having stacked capacitor cells each of which usesan n⁺ type polysilicon film as its lower electrode (storage node), atantalum pentoxide film as its capacitor insulating film, and atwo-layer film of carbon/tungsten as its upper electrode.

First, as in Example 1, a device isolation film 202, a gate oxide film203, a gate electrode 204, and n⁻ type regions 205₁ and 205₂ are formedon a p type silicon substrate 201 having a specific resistance of 10Ω·cm and the (100) plane (FIG. 4A).

Also, as in Example 1, a thick CVD oxide film 206 and an opening 207communicating with the n⁻ type region 205 are formed (FIG. 4B).

Moreover, in the same manner as in Example 1, an n⁺ type polysiliconfilm pattern 208 is formed to come in contact with the n⁻ type region205₁ through the opening 207. If necessary, a very thin silicon nitridefilm 209 may be formed by direct nitridation on the pattern 208 for thesame purpose as in Example 1 (FIG. 4C).

Next, a tantalum pentoxide film 210 serving as the capacitor insulatingfilm is deposited by reactive sputtering, CVD, or another suitable filmforming technique. Subsequently, a carbon film and a tungsten film areformed in sequence and then patterned by conventional photoresistmasking and etching to form the capacitor upper electrode consisting oflayers of a carbon film pattern 211 and a tungsten film pattern 212(FIG. 4D).

In this manner a memory cell capacitor composed of the capacitor lowerelectrode consisting of the polysilicon film pattern 208, the capacitorinsulating layer consisting of the tantalum pentoxide film 210, and thecapacitor upper electrode consisting of two layers of the carbon filmpattern 211 and the tungsten film pattern 212 is completed.

As usual, the LSI manufacturing process is followed by subsequent stepsincluding the formation of a passivation film, the formation ofconnecting wires, etc.

Now, the leakage characteristics (I-V characteristics) were evaluatedfor the capacitor of the second embodiment. For comparison, the leakagecharacteristics were likewise evaluated for a conventional capacitorhaving its insulating film made of a tantalum pentoxide film and itsupper electrode made of a tungsten film only. The results are shown inFIG. 12. As can be seen from the graph, with the same voltage applied,the capacitor of the present embodiment bring a substantial reduction inleakage current as compared with the conventional capacitor. It will beunderstood from the results that the use of a carbon film as a capacitorelectrode permits leakage current to be suppressed even when ahigh-permittivity material is used for the capacitor insulating film toincrease capacitance.

EXAMPLE 3

FIGS. 5A to 5D illustrate manufacturing steps of a capacitor accordingto a third embodiment of the present invention. The third embodiment isdirected to a DRAM having stacked capacitor cells each of which uses acarbon film as its lower electrode (storage node), a strontium titanate(SrTiO₃) film as its capacitor insulating film, and a carbon film as itsupper electrode (plate electrode).

First, as in Example 1, a device isolation film 302, an oxide film 303,a gate electrode 304, and n⁻ type regions 305₁ and 305₂ are formed on ap type silicon substrate 301 having a specific resistance of 10 Ω·cm andthe (100) plane (FIG. 5A).

Also, as in Example 1, a thick CVD oxide film 306 and an opening 307communicating with the n⁻ type region 305 are formed (FIG. 5B).

Next, a carbon film is deposited and then patterned by conventionalphotoresist masking and etching to form a carbon film pattern 308 whichis in contact with the n⁻ type region 305₁ through the opening 307 (FIG.5C).

Next, a strontium titanate film 309 serving as the capacitor insulatingfilm is deposited by reactive sputtering, CVD, or another suitable filmforming technique. Subsequently, a carbon film is deposited on thestrontium titanate film 309, and it is then patterned by conventionalphotoresist masking and etching to form a carbon film pattern 310 (FIG.5D).

In this manner a memory cell capacitor composed of the capacitor lowerelectrode consisting of the carbon film pattern 308, the capacitorinsulating layer consisting of the strontium titanate film 309, and thecapacitor upper electrode consisting of the carbon film pattern 310 iscompleted.

As usual, the LSI manufacturing process includes subsequent steps offormation of a passivation film, formation of connecting wires, etc.

EXAMPLE 4

FIGS. 6A to 6C illustrate the manufacturing steps of a capacitoraccording to a fourth embodiment of the present invention. This fourthembodiment is directed to a DRAM having stacked capacitor cells each ofwhich uses an n⁺ type polysilicon film as its lower electrode (storagenode), a tantalum pentoxide film as its capacitor insulating film, and acarbon film formed by sputtering as its upper electrode (plateelectrode). This Example involves a capacitor manufacturing methodincluding a step of annealing the tantalum pentoxide film at hightemperature in an atmosphere of active or excited oxygen.

First, the major surface of a (100) p-type silicon substrate 401 havinga specific resistance of 10 Ω·cm is selectively oxidized by LOCOS toform a thick device isolation oxide film 402. Next, a thin oxide film isformed on the surface of a device region surrounded by the deviceisolation film 402, and an n⁺ type polysilicon film is then deposited byCVD on the oxide film. Subsequently, the oxide film and the polysiliconfilm are patterned by conventional photoresist masking and etching toform a gate oxide film 403 and a gate electrode 404. The substrate 101is subsequently subjected to ion implantation using the gate electrode404 as a blocking mask, whereby n⁻ type regions 405₁ and 405₂ separatedby a channel region are formed on a self-alignment basis. The n⁻ typeregions 405₁ and 405₂ serves as the source and drain regions,respectively, of a MOS transistor. Next, a thick CVD oxide film 406serving as an interlayer insulating film is formed on the entire surfaceof the substrate and then patterned by conventional photoresist maskingand etching to form an opening communicating with the n⁻ type region405₁. Subsequently, tungsten silicide is deposited and patterned byconventional photoresist masking and etching to form a bit line 407which contacts the n⁻ type region 405₁ at the opening. Subsequently, asecond CVD oxide film 408 is deposited (FIG. 6A).

Next, subsequent to the formation of an opening communicating with then⁻ type region 405₂, a second n⁺ type polysilicon film is deposited andthen patterned by conventional photoresist masking and etching. Thereby,an n⁺ type polysilicon film 409 is formed which is in contact with then⁻ type region 405₂ at the opening. Subsequently, if necessary, a verythin silicon nitride film 410 may be formed on the polysilicon filmpattern 409 by direct nitridation in order to prevent oxide from growingnaturally on the pattern 409. Next, a CVD process using a source of, forexample, Ta(OC₂ H₅)₅, is performed to deposit a tantalum pentoxide film411 to a thickness of about 200 A (FIG. 6B).

Next, in such an annealing chamber 11 equipped with an RF electrode 12as shown in FIG. 9, a wafer 10 in the state of FIG. 6B is annealed. Inthis case, an oxygen gas is supplied by an oxygen line 13 and an RFdischarge at 50 to 300 W is performed, so that annealing is carried outin a low-pressure oxygen plasma atmosphere. The wafer is placed on aheater 14 so that it is heated to a temperature between 400°and 700° C.

Next, a carbon film is formed on the tantalum pentoxide film 411 bysputtering and then patterned by conventional photolithographic maskingand etching to form a carbon film pattern 412 used as the capacitorplate electrode (FIG. 6C). If necessary, a metal film may be formed onthe carbon film pattern.

In the manner as described above, a memory cell capacitor is completedwhich is composed of the lower electrode of the polysilicon film pattern409, the capacitor insulating film of the tantalum pentoxide film 411,and the upper electrode of the carbon film pattern 412.

The usual LSI manufacturing process will include subsequent steps offorming a passivation film, forming connecting wires, etc.

EXAMPLE 5

FIGS. 7A to 7C illustrate manufacturing steps of a capacitor accordingto a fifth embodiment of the present invention. In the fifth embodiment,which is a modification of the fourth embodiment, the capacitorelectrodes are formed in the shape of a cylinder to increase thecapacitance. This Example also includes a step of annealing the tantalumpentoxide film at high temperature in an active or excited oxygenatmosphere.

First, a (100) p type silicon substrate 501 having a specific resistanceof 10 Ω·cm is used to form a device isolation film 502, a gate oxidefilm 503, a gate electrode 504, n⁻ type regions 505₁ and 505₂, a thickCVD oxide film 506, a bit line 507, and a second CVD oxide film 508(FIG. 7A) in the same manner as in Example 4.

Next, as in Example 4, subsequent to the formation of an openingcommunicating with the n⁻ type region 505₂, an n⁺ type polysilicon filmpattern 509 is formed which is in contact with the region 505₂ at theopening. In this Example, however, the n⁺ type polysilicon film pattern509 is formed in the shape of a cylinder as shown for the purpose ofincreasing the capacitor area. Subsequently, as in Example 4, a verythin silicon nitride film 510 is, if necessary, formed by directnitridation on the polysilicon film pattern 509, and a tantalumpentoxide film 511 is deposited to a thickness of about 200 A (FIG. 7B).

Next, in such an annealing chamber 21 as shown in FIG. 10, a wafer 20 inthe sate of FIG. 7B is annealed. In this case, an anneal is performed inan atmosphere of oxygen radicals which are produced by microwavedischarge at 100 to 700 W in an microwave discharge device 21 suppliedwith oxygen and then supplied to the annealing chamber through a line22. The wafer 20 is placed on a heater 14 so that it is heated to atemperature between 400° and 700° C.

Next, a carbon film 512 is formed on the tantalum pentoxide film 511 byCVD. The CVD carbon film 512 is deposited at a thickness of about 200 Aby introducing methane gas onto the wafer in a temperature between 300and 400K and causing a chemical reaction by radio frequency (RF)discharge. Besides methane gas, ethylene, styrene, butadiene, benzene,toluene or xylene gas may be used as the CVD source. The carbon film 512thus formed is patterned by conventional photolithographic masking andetching to form the carbon film pattern 512 which is used as a plateelectrode (FIG. 7C).

In the manner described above a memory cell capacitor is completed whichis composed of the lower electrode consisting of the polysilicon filmpattern 509, the capacitor insulating film consisting of the tantalumpentoxide film 511, and the upper electrode consisting of the carbonfilm pattern 512.

The usual LSI manufacturing process includes subsequent steps of forminga passivation film, forming connecting wires, etc.

EXAMPLE 6

FIGS. 8A to 8C illustrate manufacturing steps of a capacitor accordingto a sixth embodiment of the present invention. This embodiment isdirected to a DRAM having stacked capacitor cells each of which uses afilm of platinum as its lower electrode (storage node), a film ofstrontium titanate as its capacitor insulating film, and a film ofcarbon as its upper electrode (plate electrode). This Example alsoincludes a step of annealing the strontium titanate film at hightemperature in an active or excited oxygen atmosphere.

First, a (100) p type silicon substrate 601 having a specific resistanceof 10 Ω·cm is used to form a device isolation film 602, a gate oxidefilm 603, a gate electrode 604, n⁻ type regions 605₁ and 605₂, a thickCVD oxide film 606, a bit line 607, and a second CVD oxide film 608 inthe same manner as in Example 4 (FIG. 8A).

Next, after the formation of an opening communicating with the n⁻ typeregion 605₂, a second n⁺ polysilicon film 609 is deposited and thenetched back. Thereby, the second n⁺ type polysilicon film 609 is leftburied in the opening and contacts to the n⁻ type region 605₂.Subsequently, a film of titanium nitride (TIN) is deposited over theentire surface of the wafer and then patterned by conventionalphotolithographic masking and etching to form a titanium nitride filmpattern 610 which is in contact with the second n⁺ type polysilicon film609. Further, a platinum film 611 is selectively formed only on thetitanium nitride film pattern 610 by plating, for example. Next, astrontium titanate (SrTiO₃) film 612 is formed over the entire surfaceby CVD, sputtering, or another suitable film forming technique (FIG.8B).

Next, the wafer in the state of FIG. 8B is subjected to annealing insuch an annealing chamber 31 equipped with a UV (ultraviolet) lamp 32 asshown in FIG. 11. In this case, the annealing is performed in the ozonegas supplied from a line 33 while the wafer is irradiated withultraviolet rays from the UV lamp 32. The wafer is placed on a heater 14and heated to a given temperature.

Next, as in Example 5, a carbon film is formed by CVD and patterned byconventional photolithographic masking and etching to form a carbon filmpattern 613 serving as the capacitor plate electrode (FIG. 8C).

In the manner described above a memory cell capacitor is completed whichis composed of the lower electrode consisting of the platinum film 611,the capacitor insulating film consisting of the strontium titanate film612, and the upper electrode consisting of the carbon film pattern 613.

The usual LSI manufacturing process includes subsequent steps of theformation of a passivation film, the formation of connecting wires, etc.

EXAMPLE 7

This Example relates to forming a carbon film used as a capacitorelectrode at a temperature of 300° C. or more, thereby increasing thework function of the carbon film and further decreasing the capacitorleakage current.

In this Example, the capacitor shown in FIG. 6c was fabricated inexactly the same manner as in Example 4 except that the upper electrode412 was formed in the following manner.

That is, in this Example, the carbon film 412 was formed by sputteringwith the wafer maintained at different temperatures of room temperature,150° C., 300° C. and 450° C. and then patterned into the upper electrode412.

The four types of capacitors thus obtained under the differentconditions were examined for I-V characteristics and the results shownin FIG. 13 were obtained. It will be seen from FIG. 13 that asubstantial reduction in leakage current is attained when the carbonfilm 412 is formed at a temperature of 300° C. or more.

In order to search for the cause of the results in FIG. 13, the upperelectrode of silicon oxide capacitor (MOS capacitor) was formed of acarbon film under the same conditions as described above, and the C-vcharacteristics of the resulting MOS capacitor was measured. The workfunction of the carbon film formed at each of the above temperatures wasthen obtained from a shift in the C-V curve (a shift in a flatbandvoltage). The results are shown in FIG. 14. It will be understood fromthe figure that the work function of the carbon film increases sharplyat temperatures of 300° C. or more. Therefore, a substantial reductionin leakage current seems to be caused by a remarkable increase in thework function value of the carbon film when formed at a temperature of300° C. or more and the resulting high energy barrier between thecapacitor insulating film and the carbon film.

As described above in detail, the present invention can provide asemiconductor integrated-circuit capacitor having reduced leakagecurrent and high storage capacitance because of the use of a carbon filmas a capacitor electrode. This will increase the reliability andperformance of DRAMs.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details, representative devices, andillustrated examples shown and described herein. Accordingly, variousmodifications may be made without departing from the spirit or scope ofthe general inventive concept as defined by the appended claims andtheir equivalents.

What is claimed is:
 1. A method of manufacturing a semiconductorintegrated-circuit capacitor comprising the steps of:forming a capacitorlower electrode on a semiconductor substrate; forming a capacitorinsulating film of a high-permativity material having a dielectricconstant of at least 20, on said capacitor lower electrode; annealingsaid capacitor insulating film in a gas atmosphere containing excitedoxygen prepared from an oxygen plasma or by discharge in oxygen gas; andforming a capacitor upper electrode on said capacitor insulating filmthat has been annealed.
 2. A method of manufacturing a semiconductorintegrated-circuit capacitor according to claim 1, wherein the step offorming said capacitor upper electrode includes formation of a carbonfilm.
 3. A method of manufacturing a semiconductor integrated-circuitcapacitor according to claim 2, wherein the formation of said carbonfilm is carried out at a temperature of 300° C. or more.
 4. A method ofmanufacturing a semiconductor integrated-circuit capacitor according toclaim 3, wherein the formation of said carbon film is carried out bysputtering.
 5. A method of manufacturing a semiconductorintegrated-circuit capacitor according to claim 1, wherein saidcapacitor upper electrode consists of a metal film.
 6. The method ofmanufacturing a semiconductor integrated-circuit capacitor according toclaim 1, wherein said high-permativity material is selected from thegroup consisting of silicon nitride, tantalum pentoxide, zirconiumdioxide, hafnium dioxide, niobium pentoxide, lead titanate, leadzirconate titanate, strontium titanate and barium titanate.
 7. Themethod of claim 1, wherein said capacitor upper electrode comprises atleast one member selected from the group consisting of carbon andtungsten.
 8. The method of claim 2, wherein said carbon film comprisesat least one member selected from the group consisting of boron,phosphorus and arsenic.
 9. The method of claim 2, wherein said capacitorupper electrode is a two-layer film comprising carbon and tungsten. 10.The method of claim 1, wherein said excited oxygen is prepared from anoxygen plasma prepared by a RF discharge of 50-300 W.
 11. The method ofclaim 1, wherein said high-permativity material is selected from thegroup consisting of silicon nitride, tantalum pentoxide, zirconiumdioxide, hafnium dioxide, niobium pentoxide, lead titanate, strontiumtitanate and barium titanate.
 12. The method of claim 1, wherein saidexcited oxygen comprises atomic oxygen.